Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

2. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

4.33

1.33

3.33

3. Most thermostatic expansion valves are set for a superheat of

15°C

5°C

20°C

10°C

4. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

Condenser and receiver

5. The condition of refrigerant after passing through the condenser in a vapour compression system is

Wet vapour

Dry saturated vapour

Superheated vapour

Saturated liquid

6. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

7. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

8. A thermostatic expansion valve in a refrigeration system

None of the above

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

9. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

10. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.6

0.376

0.67

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11. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Zero

None of these

Negative

12. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

13. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

14. The boiling point of ammonia is

-10.5°C

-33.3°C

-77.7°C

-30°C

15. In a lithium bromide absorption refrigeration system

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

16. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Condenser, absorber and separator (rectifier)

Absorber

Evaporator

17. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

18. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

30 bar

8 bar

15 bar

19. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Detect liquid in vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

20. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Carnot

Rankine

Reversed Carnot

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21. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

22. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Ambient air temperature

Dry bulb temperature of air

Wet bulb temperature of air

23. For obtaining high COP, the pressure range of compressor should be

Optimum

High

Low

Any value

24. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 9

1: 1

1: 3

25. The capillary tube, as an expansion device, is used in

All of these

Room air conditioners

Domestic refrigerators

Water coolers

26. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

Two heat exchangers

One heat exchanger

27. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Carbon dioxide

Freon

Brine

28. Critical temperature is the temperature above which

Water will never evaporate

Water will evaporate

A gas will never liquefy

A gas will immediately liquefy

29. Rating of a domestic refrigerator is of the order of

10 tons

5 tons

0.1 ton

40 tons

30. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

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31. Which of the following cycles uses air as the refrigerant?

Stirling

Carnot

Bell Coleman

Ericson

32. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Equal to unity

Always less than unity

Any one of the above

33. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Piston type reciprocating

Centrifugal

Axial

34. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

35. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Normal cooling

Sub-cooling or under-cooling

None of these

36. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Large latent heat

Good electrical conductor

High risibility with oil

37. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

38. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

39. The freezing point of sulphur dioxide is

-75.2°C

-56.6°C

-77.7°C

-135.8°C

40. Freon group of refrigerants are

Non-inflammable and toxic

Toxic

Inflammable

Nontoxic and non-inflammable

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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